The present disclosure relates to a storage device and a storage unit that store information by change in electrical characteristics of a storage layer that includes an ion source layer.
As semiconductor non-volatile memories for data storage, NOR-type or NAND-type flash memories have been generally used. Although a memory device and a driving transistor have been miniaturized in order to increase the capacity of a semiconductor non-volatile memory, the limitation in miniaturization has been pointed out since a high-voltage is necessary for writing and erasing and the number of electrons to be injected into the floating gate is limited.
Currently, resistance change memories such as a ReRAM (resistance random access memory) and a PRAM (phase-change random access memory) have been proposed as next generation non-volatile memories capable of breaking through the limitation in miniaturization (for example, see Japanese Unexamined Patent Application Publication No. 2006-196537 and Waser et al., Advanced Material, 21, p. 2932 (2009)). Such memories have a simple structure in which a resistance change layer is disposed between two electrodes, and it is considered that atoms or ions transfer due to heat or an electric field to form a conduction path, and thus the resistance value of the resistance change layer is changed, thereby performing writing and erasing.
A multi-value of a memory is an alternative way to increase the capacity of the memory in which writing and erasing are performed using the resistance change besides the miniaturization of the memory as described above. Allowing the multi-value of the memory, in other words, allowing a multi-value recording of 2 bits (4 values), 3 bits (8 values) etc. per device increases the capacity two-fold, three-fold, and so on.